Amplifier system



Jan. 3, 1933; WALSH 1,893,044

AMPLIFIER SYSTEM Filed NOV. 7, 1930 Afforney Patented Jan. 3, 1933 EATENT @TFICE PHILIP J. WALSH, OF SAN FRANCISCO, CALIFORNIA AMPLIFIER SYSTEM Application filed November This invention relates to an amplifier system, especially such as are used to amplify minute signaling current impulses encountered in radio reception.

In my prior Patent No. 1,594,582 I describe an amplifier system in which use is made of a pair of electronic emission devices, the impedance of one of which is varied in accordance with the signaling impulses, and which are so arranged that the sum of the currents flowing through the two devices is maintained constant, and the amplified impulses are produced by the difference in the currents flowing in the two devices.

Such a system is also generally described in my two copen ding applications, the first having Serial No. 296,140, filed July 30, 1928, and entitled Constant current amplifier sys tem; and the other having Serial No. 458,975, filed June 2, 19.30, and entitled Amplifying system.

It is an object of my present invention to improve the systems described in my prior applications and patent.

In the prior systems referred to above, the impedance of one of the two electronic emission devices is so arranged as to be controlled by the input signaling impulses while the impedance of the other device is varied oppositely to that of the first mentioned device, and in accordance with the differences existing in the space currents in the two tubes. There is thus a building up process whereby a signaling impulse causes an extreme or magnified difference in the impedances of the two electronic emission devices. It is another ob ject of my invention to simplify the apparatus needed for securing this building up process, and especially by the aid of stationary apparatus, as distinguished from the provision of a movable coil for providing an ad justable coupling between the tube circuits.

It is still another object of my invention substantially to reduce the cost of manufacturing such amplifiers.

It i s still another object of my invention to obviate the possibility of producing undesired oscillations of such amplitude as to injure the loud speaker connected to the amplifying system.

7, 1930. Serial No. 494,047.

My invention possesses .mny other advantages, and has other objects which may be made more easily apparent from a consideration of one embodiment of my invention. For this purpose I have shown a form in the drawing accompanying and forming part of the present specification. I shall now proceed to describe this form in detail, which illustrates the general principles of my invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawing:

Figure 1 is a schematic wiring diagram of one form of the system.

In the present instance I show the amplifying system in connection with a detector stage to provide a complete radio receiving system.

Furthermore, I indicate the amplified signals in as utilized in a loud speaker 1, which is of the dynamic type. This loud speaker has a dynamic coil 2. and a stationary field coil 8, connected as is well-known to produce a movement of the loud speaker diaphragm or cone in accordance with the signals received or amplified.

In the present instance, the amplifier stages and detector are affected by impulses received in a pick-up circuit, arranged to pick up radio frequency energy. This pick-up circuit is shown as including the elevated conductors 4:. a tuning condenser 5, an inductance coil 6, a variable inductance 7, a fixed condenser 8, and a ground connection 9. For use in receiving broadcast programs, the condenser 5 can be of the order of .0001 microfarads; and this condense-r as well as the variable inductance 7 can be arranged to be operated by a common shaft to which all the other tuning devices are connected as described hereinafter. The common shaft in fact can be connected to this pick-up circuit and in the diagram the connection 10 indicates this.

The impulses received in the pick-up circuit just described are transferred to a tunable circuit 11 as by coupling coil 6 to the coil 12 of this tunable circuit. This circuit 11 also includes the variable condenser 13 of about as is well understood by the signaling im-.

.0005 microfarads. The radio frequency waves picked up by the system are modulated,

pulses to be received and amplified, and the tunable circuit 11 makes it possible to differentiate between carrier waves of different frequencies. Since this process is now well understood further explanation thereof is unnecessary.

, In the first stage of amplification, these radio frequency waves with their modulations are amplified as by the aid of the two electronic emission devices 14 and 15. In the present instance, devices 14 and 15 include. respectively cathodes 16 and 17 which emit electrons that pass through the intervening space of the evacuated devices to be received 7 on the plates or anodes 18 and 19 respectively.

These plates 18 and 19 are maintained at a potential positive with respect to their respective cathodes in order to attract the electrons. The cathodes 16 and 17 can be heated by electrical heating elements 20 and 21, although other forms of producing an electronic emission may beutilized. The main purpose'is to obtain a space current formed by the electrons passing respectively from the cathodes 16, 17 to the anodes 18, 19.

It has been found that the volume of electronic flow forming the space current can be very materially varied by comparatively smallvariations in the potential of a point in the space current path, as by the aid of a control electrode such as 22, 23. These con trol electrodes are usually inthe form of grids. Therefore the signaling impulses can be utilizedto vary the potential difference between the cathode 16 and grid 22, and

comparatively large variations in the space current can be effected; and ltis upon this mode of operation that amplification 1s secured.

It is thus seen that an input circuit,-carrying relatively minute signaling impulses, can be connected between the cathode 16 and the control electrode 22; and an output circuit can be connected between the anode 18 and the cathode 16 for carrying the amplified impulses.

The tunable circuit 11 is so arranged that the electromotive forces present across either of the two elements 12 and 13 are impressed battery 26 is utilized in a well-known man ner to provide amplification on the most favorable portion of the characteristic for the tube 14-. Since this also is well understood,

further description thereof is not necessary.

Before proceeding with a description of the output circuit of tube 14, the means for heating the cathode 16 may be briefly described. This heating means is in the form, 7 as mentioned before, of a heating unit 20 supplied with current through leads 29 and 30 leading to the secondary coil 31 of a power transformer 32. This power transformer 32 has a primary coil 33 supplied with current from an alternater 34. This alternator 34 represents a form of power supply, other forms being also possible of use.

The circuit 35 between the alternater 34 and transformer 32 can be arranged, as by the aid of coils 36, condensers37- and ground 38 to reduce extraneous fluctuations. The transformer 32 is provided with further secondary coils, providing the positive potentials for the anodes used in the whole system. Thus the coil 39 is connected to a rectifying tube 40. This tube has a filament or cathode 41 heated by current as from another secondary coil 42. Since the present invention does not relate particularly to the power supply, it is sufficient to mention that the resistance-43 is supplied with direct current in such a way that its upper terminal is pcsi tive and its lower terminalis negative.- Hesistances 43 and 44 are connected in series-i between filament 41 and the center tap on coil 39, thus providing a path for the rectified current from either anode of tube 40,.through a half section of 0011 39, through these resistances, backto the cathode 41. The same l! system thus provides negative biases for the variouscontrol electrodes, as by the use of the resistance 44, the left hand terminal of which is positive with respectto the right hand terminal. p

The output circuit can now be tracedfor device'14. This output circuit includes the anode 18, a c0il'45, a coil 46, tap 47 on resistance 43, the negative terminalof resistance 43, connections 47, 48, ground connections 49 :1

and 9, and connections ode 16.

The electronic emission device 15 has an output circuit in which the current flow add- 27 and 28 to the oathed to the current flow through tube 14 re- 1 mains substantially constant. This is secured by parallelling the two space currents n the two tubes 14 and 15 through the common coil 46', having a high inductance, of about 500 millihenrys. Thus in tracing 1 the output circuit for tube 15, the tap 47 on the resistance 43 can be used as the starting point, thence coil 46, where the constant current is split into two paths; one as already traced through the space of tube 14; and the other through the space of tube 15, and including anode 19, cathode 17 connections 28, 27, ground connections 9, 49, and connections 48 and 47, to the negative terminal of resistance 43. 7

It is thus apparent that due to the provision of the coil 46, whenever the current flow increases through the space of tube 14, there must be a corresponding decrease in the space current of tube 15, since the sum of these two currents is maintained constant.

Before describing how this difference in space current flow is obtained, it may be mentioned that devices 14 and 15 are shown as being provided with screen grids and 51. These screen grids are maintained at a potential positive with respect to the cathodes 16 and 17 as by the aid of connections 52 and 53 leading to resistance 43. By providing an intermediate resistance 54 connected between points 53 and cathodes 16 and 17, the amount of positive potential on these grids 50 and 51 can be controlled as by moving the tap 55. This provides a convenient volume control, since the larger the positive potential is on these grids, the greater is the amplification. Since this system of volume control has been described in connection with my prior applications referred to above, further explanation is unnecessary. Furthermore, a large condenser 56 of about 1 microfarad can be used to connect the screen grids to the cathodes for providing a steadying effect upon the positive potentials applied to these screen grids.

It is noted in this form of my invention that the choke coil 46, which maintains the sum of the space currents constant, is connected to one terminal of the coil 45 instead of to an intermediate point in the coil. 1 find that this mode of connection is desirable, and has a steadying efiect upon the operation of the system.

In order to accentuate the difierences in space current flow in the two tubes 14 and 15 the impedance of tube 15 is affected oppositely to the impedance of tube 14. This can be accomplished by coupling a tunable circuit 57 to coil 45. This circuit includes a coil 58 in fixed coupling relation with coil 45 and having about the same inductance as coil 45. The variable condenser 59 parallels the coil 58 and forms the tunable circuit therewith. It is thus apparent that an electromotive force can be induced from coil 45 in coil 58 which can affect the input circuit of tube 15. Thus the input circuit of tube 15 can be traced from control electrode 28, circuit 57, connections 60 and 10, battery 26, and connections 27 and 28 to the cathode 17.

Coil 58 is coupled ust tightly enough with coil 45 to secure a maximum accentuation without instability.

The degree of unbalance between the two space currents in tube 14 15 can be utilized to affect succeeding stages of amplific tion operating on the same principle as the first stage. However, in the present instance I show this unbalancing effect as affecting a detector stage built in accordance with my copending application 458,975. This stage includes the two electronic emission tubes 61 and 62 similar to tubes 14 and 15 but shown as without positive screen grids. The cathodes 63, 64 are heated by elements 65, 66 supplied in parallel with the heaters 20 and 21 of the radio frequency amplifier stage. The anodes 67 and 68 are provided with a positive potential as by tap 69 on resistance 43. trodes or grids 70 and 71 can be provided for these tubes.

The input circuits of these tubes 61 and 62 include a tunable link circuit 72 coupled as by another tunable circuit 7 3 to coil 45. This coupling is preferably constant. Condensers 74 and 75 of these tunable linl: circuits can be operated from the common condensers shaft and serve to impart further selectivity to the system.

The detector tubes 61 and 62 are so arranged as to act in conjunction as full-wave rectifiers on opposite polarities of the amplified impulses present in the circuit 72, all as has been explained in my prior application. Thus the input circuit of tube 61 includes control electrode 70, circuit 72, connections 60 and 10, grid bias battery 26, ground connections 9 and 49, connections 48 and 7 6 to cathode 63. The input circuit of tube 62 is similar, except that the grid connection includes a grid condenser 77, and there is a grid leak resistance 78 between cathode 64 and electrode 71.

The output circuits of tubes 61 and 62 are also in parallel and may be traced as follows: from the positive connection 69 to a tap 79 on a potentiometer resistance 80 of about 25,000 ohms; one portion of the current then flows through the upper portion of resistance 80 through coil 81 and the Space of tube 61; the other portion of the current passes through the lower portion of the resistance 80, through coil 82 and the space of tube 62. Coils 81 and 82 form the primary of an iron cored transformer 83 which has a secondary coil 84. It is apparent that the two detector tubes 61 and 62 act concurrently to energize coils 81 and 82, and thereby to induce audio frequency electromotive forces in coil 84. Condensers 109, 110 by-pass the radio fre quency currents. In order to provide a means for securing local reception without too great amplification, there is a shunting resistance 85 across coil 84. This resistance, for long distances, is left unconnected as indicated, by providing a switch 86. For local reception switch 86 is closed, whereby the degree of amplification is reduced. This resistance 85 can be of the order of 250,000 ohms or less.

Vonnected to coil 84 is a succeeding stage of audio frequency amplifiers utilizing socalled power tubes 87 and 88 and operating on substantially the same theory as the other Furthermore, as before, control electubes heretofore described. In this case also, the signaling impulse first affects the input circuit of tube 87 which produces a disturbance in the balance between the two space currents in the tubes 87 and 88, ust as 1n the first radio frequency amplifier stage. Thus for example, the input circuit of tube 87 can quency choke coil 95, to dividing point 96,

where the current divides. Oneportion of the current goes through coil 97, anode 98 of tube 87, thence through the space of tube 87 to cathode 93. The other portion of the current from point 96 passes through the anode 99 and the'space of tube 88 to the cathode 100, the sumof these two currents being maintainedv constant. It is apparent that when a signaling impulse affects the impedance of tube 87 thecurrent through the tube 87 is correspondingly varied, and that through tube 88 is varied in an opposite direction. In order further to emphasize this difference in-the two space currents, the impedance of tube 88 is varied in accordance with the unbalance. This is accomplished by the aid of a coil 100 acting as a secondary to coil 97. This coil is bridged by a resistance 101. The input circuit of tube 88 connects acrossa variable portion of the resistance 101 so as to be affected by potential difierences depending upon the variations in current flow in coil 97. Thus the lower terminal of resistance 101 is connected as by lead 102, to a tap 103 on resistance 44L. Thence connections i7, 48 and 92 complete the connections to cathode 100. The tap 104 on resistance 101 connects as by lead 105 to the control electrode 106 of tube 88. The variable tap 103 on resistance l lprovides a negative grid bias in the input circuit.

The coil 107 to which the dynamic coil 2 is connected is coupled to coil 97 so as to be affected by the unbalance in output currents.

In this last stage of amplification, the audio frequency choke coil 95 is connected to the end terminal of the coil 97; and the buildup coil 100 is also stationary with respect to coil 97. Inthis case, of course, an

iron core 108 can be used for coupling coils 97, 100 and 107.

I claim:

1. In an amplifier system, a pair of devices the impedances of which can be varied in accordance with signaling impulses, a connection between said devices, said connection including an inductance coil,said coil being free of any substantial magnetic coupling to any other part of said connection and means for supplying a current to both devices, and connected to one of the ends of. the coil. V

2. In an amplifier system, a pair of devices the impedances of whichcan be varied in accordance with signaling impulses, means for varying the impedance of one of said devices in accordance with the signaling impulses to be amplified, a source of constant current for supplying current to both devices in parallel, an'inductance coil in series with only one of said devices, and free of any substantial magnetic coupling to any other part of said connection and connection from the source to one terminal of the coil;

3. The combination as set forth in claim 2 in which the coil 1s in series with that device of which the impedance is varied in accordance with signaling impulses.

1. The combinationas set forth in claim 2 in which the coil is in serie with that device of which the impedance is varied in accordance with signaling impulses, and with the addition of means whereby the impedance of the other device is varied oppositely with that of the said device.

5. The combination as set forth in claim 2 in which the coil is in series with that device of which the impedance is varied in accordance with signaling impulses, and with the addition of means whereby the impedance ing impulses between the electron. emitting electrode and control electrode of one of said dev1ces,'means for supplying a current to both devices in parallel through the spaces between the electron emitting electrode and the anode, a circuit connecting both anodes and including an inductance coil, said coil being free of any substantial magnetic coupling to any other part of said circuit and a connection from the current supplying means to a terminal of the coil.

7. The combination asset forth in claimfi, in which the coil is in series with that device of which the impedance is varied in accordance with signaling impulses.

8. The combination as set forth in claim 6, in which the coil is in series with that device of which the impedance is varied in accordance with signaling impulses, and with the addition of means whereby the impedance of the other device is varied oppositely with that I ance with signaling impulses, and with the coil.

In testimony whereof, I have subscribed my name.

PHILIP J. WALSH. 

